Synchronizing apparatus for cathode-ray oscillographs



All@ 3, l944- v R. BARTHELEMY 2,355,135

SYNCHRONZING APPARATUS FOR CATHODE RAY OSCILLOGRAPHS Filed Nov. 6, 1956 atented Aug. S8,

SYNCONIZING PPRATS FOR CA'EHDlE-RY OSCHJLQGRAPHS Ren Barthelemy, Fontenay aux Roses, France; vested in the Alien Property Custodian Application November 6, 1936, Serial No. 109,507 in France November 14, 1935 2 Claims.

It is known, in the production of saw-tooth" potential diierences for controlling the movement oi the luminous spot in cathode ray oscillographs, to use relaxation circuits including gas discharge tubes known as Thyratrons One of these systems used for television in which there are two scannings movements at right angles to one another known as line movement and image movement, Yconsists more particularly, in giving to the corresponding Thyratron circuits appropriate time constants to trigger .the oscillations of the line circuit by means of impulses synchronized with the transmission of the signals to be reproduced, and to trigger the oscillations of the image circuit by the passage oi'v a current in the line circuit. In these known systems the synchronizing impulse is received on the grid of the line Thyratron which it depolarizes in such a manner as to render the Thyratron conductive. p

The object of the present invention is to provide an improvement of the above-mentioned systems, which improvement is characterized by the use of the synchronizing impulses. 1n eiect in order the more readily to dierentiate, in the modulated current, the synchronizingimpulses from the variationsof current due to the analysis of the image, it has been proved to apply the synchronizing impulses to the current modulated by the image in such a manner that the variations of current due to the synchronizing impulses are of the same sense as the variations of current due to the dark parts of the image. As will be explained hereinafter this method enables the synchronizing apparatus at the receiver to be controlled bythe whole of the modulated voltage received without the necessity of separating out the synchronizing signals by means of alters or other appropriate apparatus.

Figures 1, 2, and 3of the accompanying drawing represent the curves of the lmodulated current as afunqtion of time.

Figure 4 is Va circuit diagram of a synchronizing apparatus at the receiver.

Fig. 1 shows the normal curve of the current modulated by the analysis of the image. The

parts l, 2 and 3 correspond to the bright parts v of a iine and the parts I', 2' correspond to the bright parts of the following line. On the other hand, the parts 4, 5; S, correspond to the dark parts. The mean current in is such that, for an interval equal to the analysis of an imagefthe total surfaces of the curve corresponding to the bright parts in equal to the surfaces of the curve corresponding to the dark parts. It

will be appreciated that the maximum amplitude of the dark parts, compared with the mean current in, is small compared with the maximum amplitude of the bright parts. It is on the appreciation of this fact that the present invention is based. It is known practice to insert the synchronizing impulses in the current modulated by the image in such a manner that the impulses produce current variations of the same sense as the bright regions of the image. It may thus happen that the maximum amplitude of the bright regions is close to the amplitude of the synchronizing signals. Filters are then necessary, at the receiver, to separate the signals out of the whole of the modulated current received.

According to the present invention, on the contrary, the amplitude of the synchronizing signalsis of the same sense as the dark parts of the analysis, as is shown in Fig. 2, in which l represents va synchronizing signal transmitted between two' successive lines. It will thus be seen that .this signal is clearly distinguished from the obscure' parts t, 5, 6. It is then possible to operate the synchronizing apparatus at the receiver directly by the received modulated current without the interposition of a lter. It is, in effect, suicient to polarize this apparatus in'such a manner that the obscure parts do not cause the same to function whilst the synchronizing sig-A nals bring it into action.

As shown in Figure 2 the synchronizing signals correspond to a reduction of theintensity of the modulated current which may even annul it. When the synchronizing device at the receiver consists of gas discharge tubes, considerable diiiioulties are encountered in obtaining the precise triggering of these tubes by means of 1 the annulment of themodulated current. Therefore, the present invention provides also that'the modulation. as the manmade-r, shan be Sliema;

Y the bright parts l, 2, 8 of the image correspond `the increase of security oi reception of the syn-.

to the reduction of the intensity of the modulated current (Fig. 3) whilst the dark -parts il, 5y t and the synchronizing signals 'l correspond to' an increase of the said current;

The principal advantages of this process aref chronizing impulsesithe easy separation of the synchronizing signals from the remainder of the modulation; the provision of a very precise trggering of the gas discharge tube at the receiver; protections against interference due tojthe fact that if the intensity of the synchronizing signals is twice that of the mean intensity the energy corresponding to the same four times that of the mean energy.

Figure 4 shows a. circuit diagram of a convenient synchronizing device more particularly for the reception of the modulated current of the form shown in Figure 3. This device comprises essentially two gas ldischarge tubes Th1 and Th2 controlling, respectively, the line" movement and the image movement of a cathode beam. The received'modulated voltage is applied to the terminals Ei and En and is transmitted to the terminals of a resistance Re through the intermediary of a resistance R1 and a condenser Ci. One of the terminals of the resistance Rz is connected to the earth line of the receiver and the other terminal is connected to they cathode K1 of the tube Th1. Moreover, Rz forms a potentiometer permitting the application, between the grid Gx and the cathode K1, of the whole or a part of the modulated voltage received. This application is made in such a sense that the synchronising signals, which correspond to an increase of the modulated potential received, bring about a reduction of the potential of the cathode K1 in order to render the tube Th1 conductive. When only a part of the modulated potential is applied across the grid and the cathode the potential oi l the cathode will be reduced more than the potential ot the grid or, in other words, the vpotential of the cathode with respect tothe grid will 'be reduced and the tube, will vbecome' conductive. The contact on the resistance B2 'feeding the grid G1 enables the point oltriggering of the tube Thi to be adjusted. y

The line oscillating vcircuit comprises the condenser Cz and the charging resistance Ra. An electrostatic coupling provided by the condenser C: which is very small compared to the condenser C2 is feeding the cathode K2 of the image gas discharge tube Tha associated with which is the condenser C4 and resistance R4 forming the image oscillating circuit. The capacities C5 and Cs coupling of the oscillating circuits, the feeding of the cathode without separation of the modulated signals being one of the characteristic features of the present invention.

What I claim is:

1. A synchronizing circuit for a television system comprising a gas discharge tube, a cathode, a grid and an anode in said tube, a direct current surce having positive and negative terminals. a condenser connected across said cathode and anode, a first resistor connected between the positive terminal and said anode, a second resistor having a first terminal connected to said, negative terminal and a second terminal connected to said cathode, a tap on said second resistor connected to said grid, a deector circuit connected across said condenser, and a source of synchronizing impulses having a positive terminal connected to said first terminal of the second resistor and a negative terminal connected to said second terminal of the second resistor.

2. A synchronizing circuit, for a television system comprising a pair of gas discharge tubes each having a cathode, a gridand an anode, a -direct current source` having a negative terminal, means fed from said source for causing a gradual increase of voltage of each of said anodes with respect to its cathode, line deiiector circuit con.- nected across the anode and cathode of one of said tubes, a frame deilector circuit connected across the anode and cathode-of the other o f said tubes, a ilrst resistor having a first terminal connected to said. negative terminal and a second terminal connected to the cathode of said one'of said tubes, a tap on said Ifirst resistor connected to the grid of said one of said tubes, .a second' resistor having a rst terminal connected to said negative terminal and a second terminal connected to the cathode of the other of said tubes, a tap on said second resistor connected to the grid oi' the other of said tubes, a-source of synchronizing impulses having a positive terminal connected to said first terminal of said rst resistor and a negative terminal connected to said second terminal 'of said first resistor, and a vcoupling condenser connecting the anode of said lone ofsaid. tubes to the second terminal'of said second resistor.

REN BARTrmLEMY. 

